Geologic reservoirs generally contain a matrix material, such as sandstone, sand, or limestone. The grains of the matrix material tend to compact against one another. Although the grains of the matrix compact against one another, there still may remain voids, or interstitial volume, in between the grains. Depending on the amount of compaction, these voids make up the porosity and permeability of the reservoir. Other factors affect the ultimate amount of interstitial volume and its corresponding porosity and permeability. Grains of the matrix that are lightly compressed may be in contact with one another at only a small point. This usually results in voids that are greater in volume and having more interconnection with each other. Alternatively, the grains of the matrix may be compressed such that they are slightly crushed one into another, thus greatly reducing the size and interconnection of the voids. Further, solutions may have flowed through the voids, precipitating deposits within the voids. This is typically called cementation. These deposits tend to reduce the interstitial volume and the interconnection of these voids, reducing porosity and permeability.
One way of increasing the permeability, if not also the porosity, of a reservoir is to artificially expand the space between the grains of the matrix. This may be accomplished in many ways. One way is to introduce foreign grains or particles that will open the space between the original grains. These foreign grains are shaped so as to assist in placement. Pressure is applied to the reservoir, forcing an expansion of the matrix. The foreign grains are forced into the existing matrix and the applied pressure is reduced. The matrix relaxes, locking the foreign grains into the matrix. The pressures applied may also be used to force fractures in the matrix itself, where foreign grains may be used to hold open the fractures after the applied pressure is reduced.
These methods of artificially altering the porosity and permeability of the reservoir have been largely successful in the petroleum production industry. However, ultimate petroleum production is still dependent on being able to move the hydrocarbons out of the reservoir and into the well bore.
A number of causes lead to reduced hydrocarbon production long before extraction of all the hydrocarbons in the reservoir. Reservoir pressures may drop or surface pumping means may become inadequate, resulting in decreased production. Excessive draw down may result in water being produced instead of hydrocarbons, possibly creating a water conduit that permanently cuts hydrocarbon production from recovery by the well. Excessive draw down may also result in collapse of the matrix, where the matrix itself is extracted, such as sand production, causing loss of hydrocarbon production and damage to the well.